Periodontal Disease is one of the most common diseases in older adults. Periodontal disease etiology involves altered host immune responses to subgingival insult by a complex polymicrobial biofilm that is not completely understood. Next Generation Sequencing (NGS) using culture- independent techniques to identify 16S rRNA genes, allows for more complete and detailed characterization of the complex composition and diversity of the human oral microbiome. Few studies have characterized the oral microbiome and its relation to periodontitis in large prospective cohorts of older adults over long time periods. We propose a cost-effective study to address these issues in a large existing, well-characterized cohort of postmenopausal women. Our omnibus hypothesis is that the oral microbiome composition is diverse, and that certain compositions will be associated with periodontal disease prevalence, severity and progression over time. This proposed study builds on existing data from the Buffalo OsteoPerio Study, an ancillary study to the Women's Health Initiative. We have available previously collected and frozen subgingival plaque samples from two already conducted OsteoPerio study visits at Baseline (N=1000; 1997-2000) and Year-5 post-Baseline (N=1000; 2002-2005). Also available are data from standardized oral exams including probing pocket depth, clinical attachment level and radiographic alveolar height measurements to characterize periodontal disease status, and extensive information on personal factors (e.g., smoking, dietary intake, obesity, diabetes, hormone use) and overall health status. We propose here to add a Year-15 post-Baseline re-examination (2014-2017) in 600 of these women to collect a 3rd set of samples, oral measures and personal data to explore the longer-term relationship between the oral microbiome composition and periodontal disease. Our study aims are to determine the composition and diversity of the subgingival microbiome at 3 times points; determine the extent to which the oral microbiome composition changes over time; identify which oral microbiome compositions are associated with periodontal disease presence, severity and progression over time; and determine the influence of key personal characteristics on the oral microbiome composition and its relation with periodontal disease status and progression. The proposed study fills a critical gap in our knowledge of the role of the subgingival microbiome in periodontal disease severity and progression at older ages. To our knowledge, there is no other prospective epidemiologic study as large and rich with data resources to address the cutting edge questions we propose here on the oral microbiome and its role in periodontal disease in postmenopausal women.